Preparation of 4,4&#39; dichlorodiphenyl sulfone

ABSTRACT

A process for the preparation of 4,4-dichlorodiphenyl sulfone by heating a mixture of (a) chlorobenzene, (b) chlorosulfonic acid or sulfur trioxide, and (c) thionyl chloride or phosgene to temperatures up to 220° C., more than the stoichiometric amount (based on the amount of chlorobenzene) of chlorosulfonic acid or sulfur trioxide and less than the stoichiometric amount of thionyl chloride or phosgene being employed.

The present invention relates to a novel process for the preparation of4,4'-dichlorodiphenyl sulfone.

4,4'-Dichlorodiphenyl sulfone is an important intermediate; it is usedmainly for the preparation of aromatic polysulfones and the synthesis ofbis(4-aminophenyl) sulfone, which is employed in the treatment ofleprosy and for curing epoxy resins. 4,4-Dichlorodiphenyl sulfone forthese applications must be of high purity.

4,4-Dichlorodiphenyl sulfone can be prepared, for example, fromchlorobenzene by treating it with a mixtur of sulfur trioxide anddimethyl or diethyl pyrosulfate, as in the process described in GermanPat. No. 1 087 592. Synthesis from chlorobenzene andchlorobenzenesulfonic acid is described in German Published ApplicationNo. 2 252 571; for this temperatures of from 220° C. to 260° C. arerequired, so that it is necessary to work at elevated pressures.

The best-known method for preparing 4,4-dichlorodiphenyl sulfone is bythe Friedel-Crafts reaction between 4,4-dichlorobenzenesulfochloride andchlorobenzene, with iron(III) chloride, for instance, as catalyst. Thisprocess is described in, for instance, German Pat. No. 2 704 972, andthe use of iron(III) chloride is a disadvantage here. The conversion tothe sulfone is carried out with chlorobenzene as solvent at about 140°C.; it is known from J. Am. Chem. Soc., 76, 5491 (1954) that at thistemperature iron(III) chloride also promotes the chlorination ofchlorobenzene, so that the chlorobenzene used as solvent and recycledcontains a considerable proportion of dichlorobenzenes; since these alsoform sulfones with chlorobenzenesulfochloride, they necessitateexpensive purification.

If the reaction is carried out as a single-stage reaction, starting fromchlorobenzene and without the isolation of the intermediate4-chlorobenzenesulfochloride, care must be taken that no sulfonic acid,thionyl chloride, or sulfur chlorides (these occur as impurities inthionyl chloride) remain in the reaction mixture: free sulfonic aciddeactivates the catalyst, thionyl chloride and sulfur chlorides causeunwanted side products.

The matter is aggravated by the necessity of adding dimethylformamide,to ensure complete conversion of 4-chlorobenzenesulfonic acid to thesulfochloride by means of thionyl chloride, since the carcinogenicdimethylcarbamoyl chloride is formed as a by-product. furthermore, theiron(III) chloride must be removed from the reaction product byhydrolysis; this gives a very corrosive medium, which places highrequirements on the engineering materials used, and considerablequantities of chlorobenzene get into the water,whichmeans that the wastewater must be treated.

The object of the invention was to provide a process for the preparationof 4,4-dichlorodiphenyl sulfone from chlorobenzene,sulfur trioxide orchlorosulfonic acid, and thionyl chloride or phosgene that does notrequire the addition of the catalysts iron(III) chloride andN,N-dimethylformamide. Furthermore, 4,4-dichlorodiphenyl sulfone was tobe obtained very pure and in high yield.

We have found that this object is achieved if in the preparation of4,4-dichlorodiphenyl sulfone by heating a mixture of (a) chlorobenzene,(b) chlorosulfonic acid or sulfur trioxide, and (c) thionyl chloride orphosgene to temperatures up to 220° C. more than the stoichiometricamount (based on the amount of chlorobenzene) of chlorosulfonic acid orsulfur trioxide and less than the stoichiometric amount of thionylchloride or phosgene are taken.

It is known that equal amounts of (a), (b), and (c) react to formchlorobenzenesulfonic acid at first, this being then chlorinated tochlorobenzenesulfonic acid chloride, which requires the same amount ofchlorobenzene again for the formation of dichlorodiphenyl sulfone.

Because the non-stoichiometric proportions of the starting compounds thenovel process leads to the formation of a slight excess ofchlorobenzenesulfonic acid, which catalyzes the conversion of thechlorobenzenesulfonic acid chloride to the sulfone. In the conventionalprocess an excess of chlorobenzene is employed, and the temperaturesnecessary for the formation of the sulfone are not attained; in thenovel process it is ensured that reaction temperatures of from 165° C.to 220° C. are attained. The final product is a melt consisting ofisomeric dichlorodiphenyl sulfones and chlorobenzenesulfonic acid.

In the novel process particularly favorable results are obtained if theamounts are in the proportions 1 mol of chlorobenzene to from 0.51 molto 0.63 mol--preferably from 0.54 mol to 0.59 mol--of chlorosulfonicacid or sulfur trioxide to from 0.49 mol to 0.37 mol--preferably from0.46 mol to 0.41 mol--of thionyl chloride or phosgene.

The mixture of starting compounds for the formation of4,4-dichlorodiphenyl sufone is heated to from 165° C. to 220° C.,preferably to from 185° C. to 200° C. It is expedient to add up to 40%of the total amount of chlorobenzene required while the mixture is beingheated up. The reaction time is roughly from 1 h to 6 h.

The end of the reaction can be found by determining thechlorobenzenesulfonic acid chloride content of the reaction mixture.This analysis can be carried out by thin-layer chromatography, gaschromatography, or high-pressure liquid chromatography, for example. Ifgas chromatography is employed the amount of chlorobenzene added can bemonitored, and adjusted so that at the end of the reaction the massfractions of chlorobenzene and chlorobenzenesulfonic acid chloride arewell below 1%,thus ensuring that all the chlorobenzene employed has beenconverted.

The melt, which contains isomeric dichlorodiphenyl sulfones in theapproximate proportions of 91% of 4,4'-isomer, 6% of 3,4'-isomer, and 3%of 2,4"-isomer, can be treated by, for instance, methods knownperse. Therequired 4,4'-isomer is however obtained very pure and in high yield bya novel, particularly advantageous embodiment of the novel process: themelt is diluted with alcohols or aromatic solvents, under pressure ifneeded, thus causing the 4,4-dichlorodiphenyl sulfone to precipitate.Suitable alcohols are alkanols of from 1 to 4 carbon atoms;suitablearomatic solvents are chlorobenzene and toluene, for instance.Particularly good results are obtained withmethanol or chlorobenzene asprecipitant. In a preferred procedure the melt is diluted by pouring itinto methanol, the temperature being chosen so that a pressure of aboutfrom 4 bar to 6 bar is obtained.

The solvent used for precipitation can be easily recovered from thesupernatant liquor by distillation. The chlorobenzenesulfonic acidremaining in the residue from distillation can be fed back for use ascatalyst in the reaction. If chlorobenzene is used as precipitant thesupernatant liquor can be returned direct for re-use in the reaction;since it contains the amount of chlorobenzenesulfonic acid needed forcatalysis subsequent charges should contain stoichiometric amounts ofthionyl chloride and chlorosulfonic acid.

4,4-Dichlorodiphenyl sulfone is obtained in high yield and purity by thenovel process, which can also be carried out continuously. The fact thatconversion to chlorobenzenesulfonic acid chloride does not have to becomplete is a considerable advantage, since there is thus no need to adddimethylformamide to catalyze this reaction. Another favorable point isthat the purity of the thionyl chloride does not have tosatisfy highrequirements respecting sulfur chlorides, since these do not lead to theformation of undesirable by-products (such as dichlorodiphenyl sulfides)under the conditions of the reaction.

EXAMPLE 1

629 g (5.4 mol) of chlorosulfonic acid and 547.4 g (4.6 mol) of thionylchloride are added to 1125 g (10 mol) of chlorobenzene at from 55° C. to65° C. After evolution of hydrogen chloride has stopped the reactionmixture is heated, and at 135° C. it begins to boil,with evolution ofhydrogen chloride. After 4-5 h the reflux diminishes noticeably and theinternal temperature rises to 195° C. Once this temperature is reachedthere is no detactable reflux of chlorobenzene. Gas-chromatographicanalysis of the mixture in the vessel shows that almost all thechlorobenzenesulfonic acid chloride has been converted to the sulfone:less than 1% remains.

The whole charge is cooled to 150° C. and stirred into 1 liter ofmethanol, with evaporative cooling. After cooling the precipitate isfiltered off and washed withmethanol. 944 g (71.5% yield, based on theamount of thionyl chloride) of 4,4'-dichlorodiphenyl sulfone with amelting point of 149°-150° C. is obtained. Gaschromatographic analysisof the product gives not less than 99.7% 4,4'isomer, less than 0.1%3,4'-isomer, and up to 0.2% 2,4'-isomer.

EXAMPLES 2 to 7

Theprocedure given in Example 1 is repeated with the amounts of startingcompounds given in the following table, which also gives the yields andpurities of the 4,4-dichlorodiphenyl sulfone obtained.

    __________________________________________________________________________                                    4,4'-                                                           Reac-         mass                                          Ex.                                                                              Amount of compound/mol                                                                       tion Yield/% based on                                                                       frac-                                         No.                                                                              ClSO.sub.3 H                                                                        SOCl.sub.2                                                                        C.sub.6 H.sub.5 Cl                                                                 time/h                                                                             SOCl.sub.2                                                                        C.sub.6 H.sub.5 Cl                                                                 tion/%                                        __________________________________________________________________________    1  5.4   4.6 10   18   71.5                                                                              63.5 99.7                                          2  5.2   4.8 10   32   56.3                                                                              53.6 99.5                                          3  5.4   4.6 10   26   62.2                                                                              57.8 99.6                                          4  5.5   4.5 10   20   70.8                                                                              64.3 99.6                                          5  5.7   4.3 10   17   72.1                                                                              62.6 99.7                                          6  5.8   4.2 10   15   73.4                                                                              61.2 99.7                                          7  6.0   4.0 10   14   74.5                                                                              59.6 99.7                                          __________________________________________________________________________

EXAMPLE 8

629 g (5.4 mol) of chlorosulfonic acid and 547.4 g (4.6 mol) of thionylchloride are added to 787.5 g (7 mol) of chlorobenzene at from 55° C. to65° C., and the mixture is heated rapidly to 185° C. There is noappreciable reflux. Heating is continued, and when the temperaturereaches 195° C. 337.5 g (3 mol) of chlorobenzene is added at such a ratethat the temperature of the mixture does not fall appreciably.Subsequent treatment of the charge is as described in Example 1, 953 g(72.2% yield, based on the amount of thionyl chloride) of4,4-dichlorodiphenyl sulfone of melting point 149°-150° C. is obtained.

EXAMPLES 9-15

The procedure is as in Example 8, except that the 337.5 g ofchlorobenzene is added at the temperatures given in the following table.

    ______________________________________                                             C.sub.6 H.sub.5 Cl                                                                     Reac-   ClC.sub.6 H.sub.4 SO.sub.2 Cl                                                           Yield/%                                       Ex.  added at:                                                                              tion    mass frac-                                                                              based on                                                                             Color of                               No.  temp./°C.                                                                       time/h  tion/% (GC)                                                                             SOCl.sub.2                                                                           product                                ______________________________________                                        8    195      17      0.3       72.2   white                                  9    200      16      0.2       73.0   white                                  10   210      15.5    0.2       73.3   gray                                   11   220      14.5    not detected                                                                            73.5   gray                                   12   190      18      0.3       72.1   white                                  13   185      19      1         70.6   white                                  14   175      25      3         68.8   white                                  15   165      40      8         62.3   white                                  ______________________________________                                    

EXAMPLE 16

The filtrate from Example 1 is freed from methoanol by distillation, theresidue is returned to the reaction vessel, and 562.5 g (5 mol) ofchlorobenzene is added. chlorobenzenesulfonic acid chloride is formed byadding 476 g (4 mol) of chlorosulfonic acid and 466 g (4 mol) of thionylchloride, the mixture is heated to 195° C., and 337.5 g (3 mol) ofchlorobenzene is added at such a rate that the temperature does notfall. the charge is subsequently treated as described in Example 1,giving 850 g (74% yield) of dichlorodiphenyl sulfone of melting point149°-150° C. Gas-chromatographic analysis of the product gives 99.6%4,4'-isomer, 0.3% 2,4'-isomer, and 0.1% 3,4'-isomer.

EXAMPLE 17

Molten reaction mixture obtained by proceeding as in Example 8 is pouredinto a pressure vessel containing 1.5 liters of methanol. The mixture isheated to from 110° C. to 115° C., raising the pressure to 4.5 bar, andstirred for another hour. After cooling,filtration, and washing withmethanol 931 g dichlorodiphenyl sufone containing 99.8% 4,4'-isomer andnot more than 0.1% each of 2,4'- and 3,4'-isomers is obtained.

We claim:
 1. A process for the preparation of 4,4-dichlorodiphenylsulfone which comprises heating a mixture of (a) chlorobenzene, (b)chlorosulfonic acid or sulfur trioxide, and (c) thionyl chloride orphosgene to provide a molten reaction mixture at temperatures of from165° C. upto 220° C., employing more than the stoichiometric amount,based on te amount of chlorobenzene, of chlorosulfonic acid or sulfurtioxide and less than the stoichiometric amount of thionyl chloride orphosgene.
 2. A process as claimed in claim 1 wherein the amounts are inthe proportions 1 mol of chlorobenzene to from 0.51 mol to 0.63 mol ofchlorosulfonic acid or sulfur trioxide to from 0.49mol to 0.37 mol ofthionylchloride or phosgene.
 3. A process as claimed in claim 1 whereinthe amounts are in the proportions 1 mol of chlorobenzene to from 0.54mol to 0.59 mol of chlorosulfonic acid or sulfur trioxide to from 0.46mol to 0.41 mol of thionyl chloride or phosgene.
 4. A process as claimedin claim 1 wherein part of the amount of chlorobenzene, but not morethan one half, is added to the reaction mixture as it is being heated upto a reaction temperature of from 165° to 220° C., and the remainingpart is added after reaching the reaction temperature.
 5. A process asclaimed in claim 1 wherein alcohols or aromatic solvents are added tothe melt obtained through thereaction and the 4,4'-dichlorodiphenylsulfone that precipitates on cooling is separated.
 6. A process asclaimed in claim 5 wherein the alcohols are alkanols of from 1 to 4carbon atoms and the aromatic solvent is chlorobenzene or toluene.
 7. Aprocess as claimed in claim 5 wherein the residue left after removal ofthe 4,4-dichlorodiphenyl sulfone and recover of the solvent ybdistillation is re-used for a reaction as claimed in claim 1 after thethree starting compounds have been added to it.
 8. A process as claimedin claim 5 wherein chlorobenzene is added to the melt and thesupernatant liquor left after the 4,4-dichlorodiphenyl sulfone has beenremoved is re-used for a reaction as claimed in claim 1 afterchlorosulfonic acid or sulfur trioxide and thionyl chloride or phosgenehave been added to it.